1. Technical Field
The present invention relates generally to chemical analysis of human breath samples; and, more particularly, to apparatus and methods for collecting human breath samples for accurate analysis of their chemical content, in particular their ethyl alcohol content. The invention takes advantage of the fact that the ethyl alcohol content of the air located deep in the lungs (alveolar air) is found to be in equilibrium with the ethyl alcohol content of the blood; and, by utilizing the known mathematical constant relationship between the ethyl alcohol in the lungs and the blood alcohol concentration under equilibrium conditions, a determination of the exact blood alcohol content based on the content of ethyl alcohol in the lungs can be made.
As the ensuing description proceeds, those skilled in the art will appreciate that the present invention can be used in a wide variety of diverse applications such as: (i) in law enforcement for the analysis of blood alcohol in suspected drunk drivers; (ii) in medicine for the chemical analysis of human breath for the detection or treatment of disease; and (iii) in physiological evaluation of pulmonary dysfunction.
The foregoing potential applications for use of the present invention, however, are listed as representative only, and are not limitative of the scope of the present invention as reflected in the appended claims.
2. Background Art
In the law enforcement area, it is often necessary to determine the blood alcohol concentration in units of percent weight by volume of persons suspected of driving while intoxicated (DWI). Testing of the blood alcohol content of suspected drunk drivers is not new; however, the public attitude towards drunk driving has changed in recent years from that of general apathy to an attitude of anger and concern. The public has now realized a large percentage of fatal automobile accidents are caused by drunk drivers. Groups such as Mothers Against Drunk Drivers (MADD) have organized on a national level to pressure individual states and the federal government to adopt tougher drunk driver laws. The success of the anti-drunk driving lobbies has been evidenced recently by the trend of many states to raise the alcohol drinking age to twenty-one years old. In addition, many states are requiring mandatory jail sentences for individuals convicted of firsttime drunk driving offenses. Newspapers and magazines are giving increased publicity to the vehicular death and destruction caused by drunk drivers, and to the recent legislation enacted to discourage drunk driving. State governors are using tough anti-drunk driving stances as a major campaign issue. Tough drunk driving laws have been enacted and enforced in Europe, Japan, and other countries for years; however, in the United States, this is a relatively recent phenomena.
With the prospect of jail and/or large fines facing those charged with drunk driving offenses, defendants are fighting back in court with renewed vigor. Their attack is aimed at the cornerstone of the DWI charge--viz., the accuracy of the blood alcohol test itself, and the competency of the personnel administering these tests. Obviously, the most accurate test that could be employed is analysis of a blood sample per se; but, such a test is invasive and, therefore, generally a test that cannot be utilized absent the subjects "informed consent". Therefore, the blood alcohol test most often used by law enforcement authorities involves a relatively easy-to-use, low cost, non-invasive procedure--viz., the "Breathalizer" which is based upon non-invasive analysis of a breath sample to determine the content of ethyl alcohol in the bloodstream. It is for this reason that the accuracy of the breath test for alcohol content is coming under the heaviest attack from defendants charged with driving while intoxicated.
The average human lung contains approximately 300 million small air sacs called "alveoli" which are surrounded by blood vessels. The alveoli of the lung are connected to the mouth by the trachea and a tree-like array of airways which allow for the movement of air from outside the subject's body to the alveoli in the lung. The major function of the lung is to allow for the exchange of oxygen and carbon dioxide between the blood and air within the lung. It has generally been accepted that the air content of the lung is an optimal point for measuring the amount of alcohol in the blood because the membranes of the lung are thin enough to allow rapid exchange of the alcohol between the blood and the air within the lung gas. Therefore, even though it is impossible to measure the amount of alcohol within the alveolar gas, the partial pressure of alcohol within the lung is believed to be the same as that in the blood under equilibrium conditions. Therefore a major assumption is made that the alcohol concentration in the exhaled breath, after the dead space is exhaled, is a constant value and equal to the blood value. It is also assumed that the breath alcohol concentration is equal to the lung air alcohol concentration.
The fact that the blood perfusion (flow) rate in the vessels surrounding the alveoli may vary has been known for years (References 18, 19). For most gases eliminated by the lung, the variation in matching alveolar ventilation and perfusion results in large variations of alveolar gas partial pressure (Reference 20). However, for a gas with a very high partition coefficient, such as ethyl alcohol, the variation in alveolar partial pressure due to differences in alveolar ventilation and perfusion matching is virtually eliminated (Reference 22). Therefore the expected single breath partial pressure profile for ethyl alcohol is essentially flat.
There is a difference, however, in the actual concentration of alcohol molecules within the gas contained in the lung (hereinafter referred to as "alveolar gas") compared to the concentration of alcohol molecules in the bloodstream. This difference is described by a mathematical relationship called the "partition coefficient" which is defined as the concentration of alcohol in the bloodstream divided by the concentration of alcohol in the air of the lungs at a prescribed temperature. Therefore, if a breath sample in equilibrium with the blood in the lungs is obtained, the blood alcohol concentration may be derived from the breath alcohol content by multiplying the breath alcohol concentration by the partition coefficient.
The exact value of the partition coefficient, although vital to an accurate determination of the blood alcohol content, has been open to dispute. See, for example, B. M. Wright, Breath Alcohol Analysis And The Blood/Breath Ratio, MEDICAL SCIENCE LAW, Vol. 15, No. 3, pp. 20-207 (1975); and M. F. Mason and K. M. Dubowski, Breath-Alcohol Analysis: Uses, Methods, and Some Forensic Problems--Review and Opinion, JOURNAL OF FORENSIC SCIENCE, Vol. 33, pp. 9-41 (1976). The most accurate determination of the partition coefficient, however, was found to be 1,756 at 37.degree. C. See, A. W. Jones, Determination of Liquid/Air Partition Coefficient for Dilute Solutions of Ethanol in Water, Whole Blood and Plasma, JOURNAL OF ANALYTICAL TOXICOLOGY, Vol. 7, July/August, pp. 193-197 (1983). Therefore, the partition coefficient of 2100 currently used in most breath tests results in calculated blood alcohol concentrations that are erroneously high by about twenty percent (20%).
Various techniques have been used in the past to determine blood alcohol content based upon the breath alcohol content including chemical processing, gas chromatography and infrared absorption techniques. Briefly, infrared absorption involves passing infrared waves of two discrete wavelengths within a discrete frequency band through a breath sample wherein the energy at each wavelength is measured after exiting the breath sample to determine the amount of energy absorbed at each wavelength by the molecules in the breath sample. These absorption values are then compared to known values for the absorption of ethanol and other gases at various concentrations to allow determination of the amount of ethyl alcohol in the sample tested. U.S. Pat. No. 4,268,751--Fritzlen et al discusses the use of two wavelengths of infrared energy at 3.48 microns and 3.3 microns to determine the presence of both ethanol and acetone in a breath sample. Previously, a single wavelength of 3.39 microns was utilized; but, both ethanol and acetone absorb infrared energy at this wavelength. However, since their absorption amounts differ relatively at discrete wavelengths 3.39 microns and 3.48 microns, the presence of both ethanol and acetone in the sample may be detected based upon the relative absorption of the infrared energy at these two frequencies.
For further clarification, additional descriptions of the apparatus and procedures used in infrared analysis are discussed in Harte, U.S. Pat. No. 3,792,272 and Adrian, U.S. Pat. No. 4,057,724.
A further listing of work carried out in the area of breath alcohol analysis is provided as follows:
1. R. N. Harger, R. B Forney and R. S. Baker, Estimation of the Level of Blood Alcohol from Analysis of Breath II, Use of Rebreathed Air, JOURNAL OF STUDIES IN ALCOHOL, Vol. 17, pp. 1-18 (1956); PA1 2. A. W. Jones, How Breathing Technique Can Influence the Results or Breath--Alcohol Analysis, MEDICAL SCIENCE LAW, Vol. 4, No. 4, pp. 275-280 (1982); PA1 3. A. W. Jones, Effects of Temperature and Humidity of Inhaled Air on the Concentration of Ethanol in a Man's Exhaled Breath, CLINICAL SCIENCE, Vol. 63, pp. 441-445 (1982); PA1 5. J. C. Russell and R. L. Jones, Breath Ethyl Alcohol Concentration and Analysis in the Presence of Chronic Obstructive Pulmonary Disease, CLINICAL BIOCHEMISTRY, Vol. 16, No. 3, pp. 182-187 (1983); PA1 6. J. Schwartz, C. Pinkward and A. Slemeyer, Ein nueues Verfahren zur Bestimmung des Blutalkoholgehaltes uber die Atemluft bei Bewusstlosen, (A New Method to Estimate Blood Alcohol Concentration From the Breath of Unconscious Subjects), ANAESTHETIST, Vol. 31, pp. 177-180 (1982); PA1 7. A. Slemeyer, Analytical Model Describing the Exchange Processes of Alcohol in the Respiratory System, ALCOHOL, DRUGS AND TRAFFIC SAFETY, ed. by L. Goldberg, Almqvist and Wiksell International, Stockholm, pp. 456-468 (1981); PA1 8. M. P. Hlastala, Multiple Inert Gas Elimination Technique, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 56, No. 1, pp. 1-7 (1984); PA1 9. M. P. Hlastala and D. D. Ralph, Inter-action of Exhaled Gas with Airway Mucosa, PROCEEDINGS XXIX CONGRESS OF THE INTERNATIONAL UNION OF PHYSIOLOGICAL SCIENCES, Vol. 15, p. 304 (1983); PA1 10. H. T. Robertson, R. L. Coffey, T. A. Standaert and W.E. Truog, Respiration and Inert Gas Exchange During High Frequency Ventilation, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 51, pp. 683-689 (1982); PA1 11. R. D. McEvoy, N. J. H. Davies, F. L. Mannino, R. J. Prutow, P. T. Schumaker, R. D. Wagner and J. B. West, Pulmonary Gas Exchange During High-Frequency Ventilation, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 52, pp. 1278-1288 (1982); PA1 12. A. W. Jones, Quantitative Measurements of the Alcohol Concentration and the Temperature or Breath During a Prolonged Exhalation, ACTA. PHYSIOLOGICA SCANDINAVICA, Vol. 114, pp. 407-412 (1982); PA1 13. E. R. McFadden, D. M Denison, J. F. Walker, B. Assoufi, A. Peacock, and T. Sopwith, Direct Recordings of the Temperature in the Tracheobronchial Tree in Normal Man, JOURNAL OF CLINICAL INVESTIGATION, Vol. 69, pp. 700-705 (1982); PA1 14. E. R. McFadden, Respiratory Heat and Water Exchange: Physiological and Clinical Implications, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 54, pp. 331-336 (1983); PA1 15. K. M. Dubowski, Breath Analysis As A Technique In Clinical Chemistry, CLINICAL CHEMISTRY, Vol. 20, pp. 966-972, 1982. PA1 16. M. F. Mason and K. M. Dubowski, Breath-Alcohol Analysis: Uses, Methods, and Some Forensic Problems--Review and Opinion, JOURNAL OF FORENSIC SCIENCE, Vol. 33, pp. 9-41 (1976); PA1 17. J. Levett and L. Karras, Errors in Current Alcohol Breath Analysis, ALCOHOL, DRUGS AND TRAFFIC SAFETY, ed. by L. Goldberg, Almqvist and Wiksell International, Stockholm, pp. 527-532 (1981); PA1 18. H. Rahn, A Concept of Mean Alveolar Air and the Ventilation-Blood Flow Relationships During Pulmonary Gas Exchange, JOURNAL OF PHYSIOLOGY Vol. 153, pp. 21-30 (1949); PA1 19. J. B. West and C. T. Dollery, Distribution of Blood Flow and Ventilation-Perfusion Ratio in the Lung, Measured With Radioactive CO.sub.2, JOURNAL OF APPLIED PHYSIOLOGY, Vol. 15, pp. 405-418 (1960); PA1 20. L. E. Farhi, Elimination of Inert Gas by the Lung, RESPIRATION PHYSIOLOGY, Vol. 3, pp. 1-11 (1967); PA1 21. W. S. Fowler, Lung Function Studies III. Uneven Pulmonary Ventilation in Normal Subjects and in Patients With Pulmonary Disease, JOURNAL OF APPLIED PHYSIOLOGY, Vol. 1, pp. 283-299 (1949); and, PA1 22. M. P. Hlastala and H. T. Robertson, Inert Gas Elimination Characteristics of the Normal Lung, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 44, pp. 258-266 (1978).
4. A. W. Jones, Role of Rebreathing in Determination of the Blood-Breath Ratio of Exhaled Ethanol, JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATION, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY, Vol. 55, pp. 1237-1241 (1983);
In most current breath-testing apparatus, the subject is required to breathe directly into a gas analyzer, such as an infrared analyzer described previously, which utilizes a sample from the end of the breath for analysis, hereinafter referred to as the "end-expired breath method". This method allows for the exhalation of a sufficient amount of breath gases to eliminate any air in the mouth and trachea which are assumed to have little or no alcohol content--that is, so-called "dead space gas"--such that the sample of alveolar gas is taken from the latter part of the exhaled breath. The end-expired breath method assumes that the alcohol concentration of the exhaled breath after elimination of the dead space gas is a constant value and proportional to the blood alcohol content.
Recently, however, it has been shown that the alcohol concentration in the breath is not constant but, rather, changes continuously as the subject exhales. See, e.g., Reference Nos. 1 through 7, supra. In the majority of studies, in fact, the alcohol concentration was found to increase as the subject exhaled. To explain this phenomenon, recent observations have found that highly soluble gases interact with the subject's airways during inhalation and exhalation. See, e.g., Reference Nos. 9 through 11 supra. During inhalation, as the inhaled cooler air from the outside is brought into the lungs, it is warmed by the transfer of heat from the tissues of the subject's airways. See, e.g., Reference Nos. 12 through 14, supra. The heat transfer between the subject's airways and the inhaled/exhaled breath results in partial condensation of alcohol over the tissues of the airway, changing the concentration of ethyl alcohol in the breath.
Early studies of the end-expired breath method of breath analysis have produced data which bear reasonable correlation to the concentrations of ethyl alcohol obtained through blood sample tests. Because of changing breath alcohol concentrations, however, random breath samples yielded average values which correlated to the blood sample concentration even though variations as much as fifty percent (50%) occurred in individual measurements. See, e.g., Reference Nos. 16 and 17, supra. These measurements were made, however, by instruments which ignored the interaction of breath alcohol with the tissue of the subject's airway.
The article by A. W. Jones entitled "The Role of Rebreating in Determination of the Blood/Breath Ratio of Expired Ethanol" (Reference No. 4), discloses that temperature gradients between the subject's lungs and mouth result in the exchange of water-soluble agents such as ethyl alcohol with the (37.degree.of the subject's airways resulting in inaccurate measurements when the end of the expired breath was analyzed. Jones indicates, however, that the concentration of ethyl alcohol in end-expired air will be less than that found in the alveolar gas. Jones utilized a rebreathing procedure to reduce the temperature gradient across the airways and trachea in an attempt to achieve a steady state breath temperature of approximately 35.2.degree. C., which then was mathematically adjusted to 37.degree. C., in an attempt to provide a more accurate estimation of the alveolar level of ethyl alcohol. This mathematical adjustment was based upon a supposed linear relationship between expired breath temperature and the blood/breath partition coefficient. Jones' mathematical adjustment to 37.degree. C. is inaccurate however, because the airways and trachea comprise a dynamic system where equilibrium conditions do not exist. Jones' rebreathing technique required the subject to breathe into a heated polyethylene bag one to five times, with the final exhalation made into a separate breath analyzing instrument which recorded the breath temperature, exhaled volume and breath alcohol concentration.
In addition to the foregoing problems, those skilled in the art have experienced many other significant problems when attempting to collect breath samples for chemical analysis. Due to the high vapor content of typical breath samples collected, there is a substantial likelihood of condensation of such vapor onto the walls of the sample collecting receptable resulting in additional inaccuracies.
In the aforementioned article by R. N. Harger et al entitled "Estimation of the Level of Blood Alcohol From Analysis of Breath--Use of Rebreathed Air" (Reference No. 1), a polyethylene bag was utilized for a rebreathing procedure. In an attempt to eliminate any moisture condensation within the sample bag, the bag was initially placed inside an incubator sack heated to 45.degree.-50.degree. C., remaining inside until the sample bag reache a temperature of approximately 45.degree. C. The bag was then removed from the incubator sack; the subject rebreathed five times into the bag; the bag was then returned to the incubator sack and evacuated to a sampling ampule tube. A disadvantage with Harger's method of preventing condensation is that the temperature of the breath sample inside the bag is neither measured nor controlled when the sample bag is outside the incubator sack. Therefore the temperature of the breath sample may fall below the dew point temperature causing condensation within the sample bag.
Additional problems occurring when using conventional breath collection methods and apparatus include the resistance offered by a narrow breathing tube to the flow of exhaled air therethrough, a so-called "back pressure". This back pressure increases the alveolar pressure making it difficult for people with lung diseases or defects to provide a breath sample of sufficient volume to include air from the deep lung area. The problem is further exacerbated by the fact that the increased alveolar pressure causes an alteration in the pattern of emptying the lungs resulting in differences in alcohol concentration in the breath sample.
Although it has been recognized that temperature gradients within the mouth, trachea and airways introduce errors into the determination of blood alcohol content from breath sample analysis, conventional methods and apparatus as described in the aforesaid references have failed to achieve a solution for eliminating the problems induced by such temperature gradients. Nor have such conventional systems provided solutions for the aforesaid condensation and back pressure problems. Therefore, prior to the advent of the present invention, there has remained an urgent need for improved methods and apparatus for determining the blood alcohol content from a breath sample which can be collected and analyzed at the proper temperature and which overcomes the problems associated with condensation and resistance to the subject's exhaled breath.